1. Field of the Invention
The present invention generally relates to a loudspeaker, and more particularly relates to a folded transmission line loudspeaker.
2. Related Art
Transmission Line (“TL”) loudspeakers are a class of open-ended, or “ported” loudspeakers that perform as a phase inverter for the low frequencies, allowing the energy of the rear of the woofer cone to be combined with the energy of the front of the cone to enhance the low frequency performance of the system. The length of the “line” or audio transmission passage is typically set equal to the one quarter of the wavelength of the frequency of the free air resonant frequency of the driver. Therefore, this type of loudspeaker is sometimes referred to as a “Quarter Wave Tube.”
One problem with transmission line loudspeaker design is the available space in the speaker system. A linear quarter wave tube would have a line length of nearly 34 inches for a driver having a free air resonant frequency of 100 Hz. Folded audio transmission passages have been proposed in the past but generally do not fit easily into modern manufacturing processes and are usually more expensive to build and larger than other known loudspeaker designs. The size of such devices typically makes them unsuitable for compact devices such as desktop computer speakers and portable media players.